Relays are typically electrically controlled devices that open and close electrical contacts to affect the current flow in an electrical circuit or the laser path in the fiber optical system. Relays are widely used in telecommunications, radio frequency (RF) communications, portable electronics, consumer and industrial electronics, aerospace, optical fiber communications, and proximity sensing systems.
A common electro-mechanical relay comprises an electromagnetic mechanism, an armature, and a contact mechanism having a fixed contact and a movable contact which are selectively closed and opened by a pivot motion of the armature. Conventional mechanical relays are manufactured individually and they are large in size. As a trend of the industry, some applications including automated testing, telecommunications and consumer electronics require higher density of relay deployment. Large size relay no longer meets the requirements.
Micro-electro-mechanical systems (MEMS) technologies provide new manufacturing methods to make micro relays. A bi-stable, latching relay that does not require power to hold the states is therefore desired. Various designs of micro magnetic relay have been disclosed.
A non-volatile programmable switch is described in U.S. Pat. No. 5,818,316 issued to Shen et al. on Oct. 6, 1998, the entirety of which is incorporated herein by reference. The switch disclosed in this reference includes first and second magnetizable conductors. The first conductor is permanently magnetized and the second conductor is switchable in response to a magnetic field applied thereto. Programming means are associated with the second conductor for switchably magnetizing the second conductor so that magnetic attraction or repulsion force can be achieved.
Another non-volatile micro relay is described in U.S. Pat. No. 6,124,650 issued to Bishop et al. on Sep. 26, 2000, the entirety of which is incorporated herein by reference. The relay employs a square-loop latchable magnetic material with its magnetization direction being changed in response to an external magnetic field. A conductor assembly creates the external magnetic field to switch the magnetic material to the desired polarization. The attractive or repulsive force between the magnetic poles keeps the switch in the closed or open state.
Yet another non-volatile micro actuator is described in U.S. Pat. No. 7,106,159 issued to Delamare et al. on Sep. 12, 2006, the entirety of which is incorporated herein by reference. The device disclosed in this reference employs a mobile permanent magnet which can be switched from one attraction zone to the other by selectively heating one of the fixed magnetic parts above the Curie temperature. Lateral contact is made when the switch closes.
Yet another non-volatile micro relay is described in U.S. Pat. No. 7,482,899 issued to Shen et al. on Jan. 27, 2009, the entirety of which is incorporated herein by reference. The device disclosed in this reference employs thin permanent magnet deposited on the movable cantilever. By selecting the polarity of the coil current, a momentarily coil current generated perpendicular magnetic field forces the cantilever to rotate to one of its two stable positions.
Each of the prior arts, though providing a unique approach to make latching electromechanical relays and possessing some advantages, has some drawbacks and limitations. Some of them only produce very small contact force limited by the material. Some of them may require large current for switching. Some require precise placement of the mobile magnet or direct manufacturing of the mobile permanent magnet on the movable structure which requires high temperature and high pressure. In general, permanent magnet with high temperature stability is brittle and easy to break. It could become a reliability concern if it is used as a moving part which experiences millions of cycles of impact during the service. These drawbacks and limitations can make manufacturing difficult and costly, and hinder their value in practical applications.
Yet another latching relay is described in U.S. Pat. No. 6,469,602 B2 (and its continuation patents) issued to Ruan et al. on Oct. 22, 2002, the entirety of which is incorporated herein by reference. The relay disclosed in this reference includes one soft magnetic cantilever, one substantial planar magnet with its magnetic field perpendicular to the cantilever's neutral position plane, and an electromagnet or a coil to provide the switching field. The magnetic cantilever exhibits a first state corresponding to the open state of the relay and a second state corresponding to the closed state of the relay. The perpendicular magnetic field from the magnet induces a magnetic torque in the cantilever, and the cantilever may be switched between the first state and the second state with a second magnetic field generated by a coil formed on a substrate of the relay. The physics is that a magnetic moment m (a vector) of the soft magnetic cantilever experiences a torque in an approximately uniform magnetic field B (also a vector), and the magnetic torque equals m×B (cross product of two vectors). As a result, the torque tends to rotate and align the cantilever with the external magnetic field lines. Other applications like sensors were also found based on this invention.
To operate the device properly, the cantilever needs to be in an approximately uniform magnetic field. Thus it requires the length of magnet to be substantially larger than the cantilever's length to provide the approximately uniform perpendicular field to actuate the cantilever. Or it needs to be positioned far away from the magnet to get the relative uniform field, which is often weak and results in undesirable performance of the device. Special techniques can be used to generate a uniform magnetic field. But a substantial size magnet is always needed, which causes long range magnetic field interference on the neighboring relays, magnetic devices or tools. Due to the magnetic interference, the dense deployment of the relays on the printed circuit board is prohibited. Shrinking the device size, especially the magnet, is difficult. The reason is that aligning the cantilever with the magnetic field line, which curves dramatically and often points in different directions near small magnets, becomes impractical.
When the magnet is small, the nearby soft magnetic cantilever sees an extraordinary non-uniform magnetic field B in terms of its magnitude and direction. Therefore, the gradient of the magnetic field is significant and the magnetic force (m·∇)B (dot product of vector m and the gradient of vector B) dominates the movement of the cantilever. The magnetic torque m×B becomes secondary. Therefore, it is an object of the present invention to provide a relay that fully utilizes both the magnetic force (m·∇)B and torque m×B. It is also the object of the present invention to provide a new type of latching micro relay that has: high contact force, small magnet size, low magnetic cross interference, small device size, high device density, high reliability, and high tolerance of process variation in the manufacture. The new relay should be easy to switch and manufacture.